The present invention is directed to a lapping device for surface enhancement of bulk material, particularly for pretreatment of the bulk material which is to subsequently receive an aluminum coating which is to be electro-deposited from an aprotic, oxygen-free and water-free, aluminum-organic electrolyte. The lapping device includes a treatment chamber in which the relative motion can be created between the bulk material and the lapping abrasive.
It should be understood that the term "lapping" is directed to a cutting process or method, wherein loose grains are distributed in a paste or a liquid as the lapping abrasive. In comparison thereto, grinding involves a cutting process or method, wherein multi-cutter tools having a geometrically defined cutter shape and the tool is formed by a plurality of grains bonded together.
Lapping devices are known, for example, from the periodical Galvanotechnik D-7968 Saulgau, Vol. 76, 1985, No. 1, Pages 67-68. In the lapping device which is referred to as vibratory grinding systems, the processing occurs in a moving fill of work pieces and grinding members. The processing in such lapping devices, which can be fashioned as drums, bells, vibrators, centrifugal systems and drag grinding systems, presumes a relative motion between the work piece and the grinding members which can proceed uncontrolled and both tangentially as well as normally relative to the surface of the work piece.
U.S. Pat. No. 3,935,680 discloses a lapping device for service enhancement of bulk material, wherein a compound composed of the material and abradants is introduced into a circular vibrating pipe and is compressed therein by the decreasing cross section of the vibrating pipe. The filling aperture of the vibrating pipe is closed during the operation with the closing only serving the purpose of allowing a greater quantity of the material to be placed in the pipe during the process. Since the vibrating pipe must be placed in vibration together with the material contained therein and the abradant, the structural size of the lapping device is limited. Accordingly, the output which can be achieved is correspondingly low.
The use of known lapping devices especially occurs during electro-plating processes for the general enhancement of the surface condition of the work piece with the goal of guaranteeing a well-adhering electro-deposits during a following galvanic deposition. Depending upon the initial condition of the work piece, the surface enhancement to be undertaken can include an edge rounding, smoothing, burnishing, polishing, degreasing and descaling. Further areas of application for the known lapping devices are surface enhancement for a following metallization in a vacuum, for the application of lacquer layers and for other methods of coating workpieces with usually extremely thin, protective and beautifying coatings on a less valuable substrate.
Given any suitable materials, the surface enhancement achieved in the known lapping devices are very quickly cancelled due to contact with air and atmospheric humidity. As a result of surface reactions, such as oxidation, corrosion and the like which reactions begin before the introduction of the work piece into the electrolytic bath, the precondition for well-adhering electro-deposits are at least considerably detereorated.
Aluminum deposited from aprotic, oxygen-free and waterfree, aluminum-organic electrolytes are distinguished by its ductility, low number of pores, corrosion resistance and ability to be anodized. Since, due to the reaction with atmospheric oxygen and atmospheric humidity, the access of air will cause a considerable reduction in the conductivity and in the usefulness of the electrolytes, the electro-plating must be undertaken in a treatment facility working under the exclusion of air or in a protective atmosphere. In order for the access of air to be prevented when loading and unloading, these treatment facilities, which operate under the exclusion of air, have admision and discharge locks which may be designed as gas locks, liquid locks or combined gas-liquid locks. These admission and discharge locks may be equipped with conveyor means for conducting the material to be electro-plated through the lock. Such aluminizing facility or apparatus operating under the exclusion of air and provided with admission and discharge locks for mass electroplating of bulk material is disclosed for example in the U.S. Pat. No. 4,427,518 which claims priority from the same German application as European patent No. 0,070,011.
An aluminum plating operation, which utilizes an aprotic aluminum-organic electrolyte, requires an especially careful pretreatment and surface enhancement of the material to be aluminized. First, no surface reactions which will deteriorate the adhesion of the aluminum layers dare occur between the pretreatment in a lapping device and the introduction of the material to be electro-plated into the aluminization device. Secondly, an entrainment of atmospheric oxygen, atmospheric humidity and other substance, which are harmful to the sensitive electrolyte, together with the material to be electro-plated must be prevented. For the above reasons, there has heretofore not been any success of providing materials for electro-depositing composed of material such as iron, steel, titanium and the like with adhering, galvanic aluminum coatings immediately after the pretreatment in a lapping device. An electro-deposited intermediate layer of nickel had to be previously applied in order to obtain a well adhering aluminum coating.